Method of forming multiple curved panels



May 3, 1960 B. SHWAYDER METHOD OF FORMING MULTIPLE CURVED PANELS FiledJuly 5. 1957 INVENTOR.

BEN SHWAYDER BY G Q & m

I ATTORNEYS METHOD OF FORMING MULTIPLE CURVED PANELS Ben Shwayder,Bloomfield Hills, Mich., assignor to Shwayder Bros. Inc., Detroit,'Mich.

Application July 5, 1957, Serial No. 670,333

1 Claim. (Cl. 18--56) This invention relates to a method of formingmultiple curved panels and more particularly to a method of bending andforming flat panels or sheets, of the type which normally resist bendingand normally tend to elastically return into their previous flat shapeafter bending, into multiple curves and bends which are permanently setin their bent condition.

The present application is a continuation-in-part of'my copendingapplication Ser. No. 577,396, filed April 10, 1956, now abandoned.

In the construction of bent or shaped panels, as for example for chairseats, fiat panels, such as plywood, hardboard, or certain types ofplastics, are pressed in dies under heat and pressure to impart adesired bent shape or indentation to such panels. However, it has beenfound that after the die pressing operation has been atent completed,the panels tend to spring back into their original flat form. Likewise,many of these flat panels resist bending altogether, and thus cannot bebent into deep curves or multiple curves, i.e., curves in two or moredirections.

' Thus, it is an object of this invention to provide a method forbending and forming and permanently setting a panel into deep curves andcompound curves, where the panel is of the type which normally resistsbending under heat and pressure and which normally tends to return toits undeformed condition after deformation.

Another object of this invention is to provide a method for bending andforming and permanently setting panels as mentioned above, and at thesame time providing an outer, protective plastic type covering for thepanel wherein panels which are of some inexpensive, relativelyunattractive, and difiicult to bend, material can be utilized.

These and other objects of this invention will become apparent afterreading the following description, of which the attached drawings form apart.

Referring to the drawings, in which:

Fig. 1 illustrates a perspective view of a finished, shaped panel bentinto compound, deep curves and which in this case, is suitable for useas a chair seat.

Fig. 2 is a front view of the perforated flat sheet forming the panel.

Fig. 3 is an enlarged cross-sectional view taken on line 3-3 of Fig. 2and illustrates the perforations or holes formed in the sheet.

Fig. 4 is a cross-sectional view similar to Fig. 3 but shows the outersheet bent and the holes distorted.

Fig. 5 shows a vertical cross-sectional view of a portion of the sheetin a forming die, and,

Fig. 6 illustrates a vertical cross-sectional fragment of the panelafter release from the forming die.

Fig. 7 shows a vertical cross-sectional fragment of a modification,wherein the sheet is covered with outer protective plastic layers.

The method In Fig. 1, a deeply bent, compound curved panel 10, suitablefor use as a chair seat, is shown. This panel is formed of a flat sheet11 of a relatively inexpensive material such as ordinary plywood, orhardwood, such as that known and marketed under the trade name Masonite,or particle board formed of wood particles and a resin binder, or thelike.

These materials are all readily available, but all have the commoncharacteristic of strongly resisting deformation, even under heat andpressure, and of tending to elas tically return to their original fiatshape after deformation. Thus, in the absence of the method of thisinvention, these materials could not be used for panels where deep bendsand multiple curves are desired.

The method herein consists first of perforating the sheet with numerousclosely spaced holes in the areas of the sheet to be bent. The holes orperforations 12 extend through the sheet 11, as. seen in Fig. 3, andpreferably are quite small in diameter, normally being longer in theirdirection transverse of the sheet than in the hole width direction takenalong the plane of'the sheet. The holes may be punched or drilled intothe sheet and enough holes are provided to weaken the sheet, that is, toreduce the resistance of the sheet to deformation in the areas to bedeformed. Thereafter, the holes are filled with a liquid resin substance14 of a type which will harden and set under heat and pressure. Next,the sheet is deformed, in a suitable set of dies 15 and 16 under heatand pressure, into the desired deep bends and compound curves.

In the dies, the hole walls are deformed, as shown in Fig. 4, and thus,the resin which fills the holes is thermally hardened into the deformedcontours of these walls. After, the resin has set, the dies are releasedand the hardened plastic acts as plugs in the holes to maintain theholes in their deformed shape and to thereby maintain the sheet in itsbent and curved shape. In this finished condition the sheet ispermanently retained in the desired shape against any resilient tendencyof the sheet to return to its original shape.

The resin One resin found to be suitable for this method is given, inparts by weight, as follows: 58 parts of polyester resin Plyothen, whichis identified as Reichold No. 8006 polyester resin, a glycolphthalic-maleic anhydride reaction product; 40 parts calcium carbonate,as a filler; 0.5 part benzoyl peroxide; 1.5 parts styrene monomer.

The holes 12 may be filled with resin before the sheet 11 is placed inthe mold or they may be filled by pouring the liquid resin in while thesheet is in the mold. The resin may be cured and the sheet bent at acuring pressure of 70-300 psi. and a temperature range of 200- 300 F.for a sufiicient length of time to harden the resin, depending upon theamount of filler and other variable operating conditions.

Many other types of synthetic resin materials may be substituted forthat resin specifically named above. Thus, for example those syntheticresins identified by the generic names of epoxy, phenolic, melamine,silicone, and similar thermo-setting resins may be employed instead ofthe polyesters specifically identified above. While the thermo-settingresins are preferred, it is also possible to use thermo-plastic resinsin connection with this invention, such as polystyrene, or polyvinylchloride. .Where a phenolic resin is employed, satisfactory results maybe employed with many of the polymerizable phenol formaldehyde resinsproduced by the Carbide and Carbon Chemicals Corporation. For example,the carbide and carbon resin designated as Bakelite XRS 17582 is a verysatisfactory phenol formaldehyde resin. Good results may be obtainedwhere this particular resin is formulated with one part of styrene forevery ten parts by weight of the Bakelite resin, with 2% to 3% benzoylperoxide being employed based on the weight of the Bakelite resin.

Outer coatings Where desired, in some cases, to protect and strengthenthe sheet 11, an outer plastic layer 13 may be bonded to the sheet atthe same time that the resin in the holes 12 are hardened. The outerlayer gives the added advantage of providing a good looking, waterimpervious, surface to the sheet so that the sheet itself may be ofinexpensive, rough appearing material, but the finished panel will beattractive and extremely strong.

While many types of plastic materials may be selected for use in theouter layer, one example of a suitable material is a mat of loosefibrous glass of A to 1 /2 ounces per square foot of O.C.S. type 503,impregnated with a liquid resin composition, such as the polyesterexample, given above,.or any of the other suitable resins mentioned.

It is desirable to have a resin which, when combined with the fibers,will be of high impact resistance, high tensile strength and waterimpervious. Also, the percentage of resin to fibrous glass may be variedconsiderably, but it is essential to use a sufficient amount tothoroughly penetrate the fibrous mat, coat the individual fibers, andfill in the perforations 12 in the sheet 11.

In molding the laminate, the perforated sheet 11 is desirably placeddirectly in the mold, and the resin is then poured over the sheet in asufiicient quantity to coat each surface of the inner layer 11 and filleach of the perforations 12. Preferably, the resin-forcing mat is placedin position on the inner layer 11 before the inner layer 11 is placed inthe mold. If convenient, the mat may be impregnated with the resinformulation before placing in the mold.

With the specific polyester formulation identified above, laminated witha glass mat on each surface thereof having a weight of oz. per squarefoot O.C.S. type 503, and an inner layer of /a" thick Masonite, a curefor minutes at 230 F. under a pressure of 100 psi. produced anexceptionally fine product, having good strength characteristics, adesirable appearance, light weight, and resistance to abrasion andchemical attack.

Regardless of the molding material employed, it is desirable that theouter layer of resin 13 be of suflicient thickness to provide aclearly-defined film over the entire surface. Best results are obtainedwhen this clearlydefined film has a thickness of at least 0.0035

As illustrated in Fig. 5, this invention is specifically directed to themolding of a sheet formed of a resilient, elastic material which, in itsfinal molded shape, is deformed from its normal state. The resin fillingthe perforations 12, after the molding operation has been completed, isintegral with the resin in the surface film, and results are integralwith any resin which may have penetrated into the sheet 11. Dependingupon the viscosity of the sheet 11, and its time of contact with theimpregnating resin, the sheet 11 may or may not be somewhat impregnated.The forming dies 15 and 16 press the laminate into the desired shape andmaintain it at the desired molding pressure and temperature during thecuring operation. After the curing or molding has been completed, theproduct is completely encased by a film of plastic material which inmany areas of themolded object penetrates completely through the objectat the per.- forations thereof.

The use of a fiber glass mat as the reinforcing agent for the plastic ispreferred because of the excellent bonding characteristics and highstrength impartedv to the molded product bythis material. Howevensimilarfibrous reinforcing agents may be substituted for the fiber glass matwith good results. Such materials as sisal and horse hair may beemployed, for example.

During the molding operation, it has been found desirable to use aparting agent on the forming dies 15 and 16, to avoid any adhesion ofthe resin to the die surfaces. If desired, cover sheets of cellophanemay be employed over the mold faces for this purpose.

Conclusion In the drawings, the perforations '12 are generally shown ingreatly enlarged form. When the panel is distorted by the forming molds,the perforations 12 become distorted usually with the part of theperforations at the outside of the bend being stretched and the part atthe inside of the bend being compressed. This effect of the distortionis shown in Fig. 4. The fluid material filling these perforationsassumes their shape, so that the perforations, though distorted, stillremain filled (see Fig. 5).

During the curing and molding operation, the material filling theperforations quickly sets or hardens. Thus, the perforations arerestrained from returning to their original shapes and the panellikewise becomes permanently set in its bent shape.

The perforations also function to provide areas in the panel where thepanel is initially weakened, e.g. before the material filling theperforations is set, thus permitting the panel to be easily bent andshaped.

This invention may be developed within the scope of the following claimswithout departing from the essential features of said invention.Accordingly, it is desired that the specification and drawings be readas being merely illustrative of a practical embodiment of the same andnot in a strictly limiting sense.

' I claim:

A method for forming permanent multiple curves in selected areas of apanel which is formed of a thick, flat sheet of wood-like, fibrousmaterial, such as plywood, hardboard and the like, which material is ofthe type which has a substantial resistance to bending and whichelastically springs back a substantial degree to its flat, unbeat shapeafter being bent, said method comprising essentially the steps ofperforating the sheet with numerous holes, extending through the sheetfrom one face of the sheet to the opposite face thereof andsubstantially perpendicular to the plane of the sheet, the holes beinglocated in the area of the sheet which is to be bent into curves andbeing in sufficient number of weakenthat area and reduce the resistanceof that area to bending, and with the holes each being of a size toundergo substantial deformation of the walls defining each hole when thesheet area is bent and each being of a length at least as great as itsdiameter and each being. of a size to receive and retain a fluid resinsubstance; filling the holes with a fluid resin substance characterizedby being normally in a liquid state and being thermosetting into arigid, solid state and being non-deformable from its solid statephysical dimensional condition; applying sufficient pressure to theselected areas of the sheet to bend those areas into the desired curvesand simultaneously to deform the walls of the holes, and thermallysetting said resinsubstance into into its solid state while maintainingsaid pressure so that the deformed wallsof each hole act' as a mold forthe resin contained in that hole and the resin solidifies into plugswhich externally conform to the shape and size of the deformed walls,and then releasing said pressure whereby the plugs fix the walls of theholes in their deformed shape and thus retain the bent curvesin thesheet and prevent the curved areas from springing back towards theirflat, unbent shape.

References Cited in the file ofthis patent UNITED STATES PATENTS 287,146Martin Oct. 23, 1883 (Other 'references on following page) UNITED STATESPATENTS Holtzman Jan. 10, 1905 Bronson Sept. 13, 1932 Aalto, June 2,1936 Schmerhorn Apr. 11, 1939 Tully Aug. 26, 1941 Libberton Mar. 24,1953 6 Khndzorian-Iablokofi et a1. Apr. 6, 1954 Cadman et a1 Jan. 17,1956 De Swart July 23, 1957 FOREIGN PATENTS Great Britain Nov. 25, 1937Great Britain June 16, 1947

